Process and apparatus for recovering clean water and solids from aqueous solids

ABSTRACT

Process and apparatus for recovering clean water and solids from aqueous solids. Aqueous solids are mixed with a low viscosity, relatively volatile, water-immiscible light fluidizing oil to obtain a mixture which will remain fluid and pumpable after removal of essentially its entire water content. The mixture of solids, water and fluidizing oil is subjected to a dehydration step by heat evaporation whereby substantially all of the water and at least part of the light oil are evaporated and subsequently recovered. The light fluidizing oil is then largely separated from the solids. Those solids carrying residual light fluidizing oil are then brought into direct contact with steam, referred to herein as &#34;blowing steam&#34;. The presence of the blowing steam reduces the boiling point of the water-immiscible light fluidizing oil to effect its more efficient removal from the solids. Effluent blowing steam and light oil vapor removed from the solids may be used to supply heat to the overall process.

This is a division of application Ser. No. 719,515, filed Sept. 1, 1976.

BACKGROUND OF THE INVENTION

The economic disposal of waste solids and recovery of clean water fromaqueous solutions and dispersions thereof is a recognized problem. Also,the need to recover clean water and valuable solid materials fromaqueous solutions and dispersions thereof is a common occurrence.Ideally, apparatuses and processes for the recovery of water fromaqueous solids should provide ease of disposition of all constituents,avoidance of pollution, economic operation and hygienic handling, andshould, in addition, yield clean water. Furthermore, in the course ofrecovering clean water it is desirable to obtain by-products, both solidand liquid, which are either valuable in themselves or can be utilizedto further the economics of the process. For purposes of this inventionit is to be understood that the term "aqueous solids" is employedgenerically to include suspensions, dispersions, solutions, mixtures andother forms of fluid association of solids in water.

In our U.S. Pat. No. 3,855,079 titled "Process and Apparatus forRecovering Residual Oil from Solids Dehydrated in an Oil Medium andGrossly Deoiled" are described process and apparatus whereby aqueoussolids are admixed with a relatively non-volatile fluidizing oil to forma mixture which is dehydrated by heat evaporation. The substantiallyanhydrous solids in fluidizing oil slurry thus formed is thereafterseparated into the oil phase and the solids phase. However, the solidshave sorbed thereon appreciable amounts of fluidizing oil whichcontaminates the solids and which will be lost to the process andcontribute to unfavorable economics if not recovered. Accordingly, thefluidizing oil-laden solids are subjected to a subsequent extractionstep using a relatively volatile, water-immiscible light oil. The lightoil-laden solids are then brought into direct contact with blowingsteam. The presence of the blowing steam reduces the boiling point ofthe residual waterimmiscible light oil to effect its more efficientremoval from the solids.

SUMMARY OF THE INVENTION

The process and apparatus of this invention comprise a series of stepsand a systematic arrangement of equipment for recovering clean water andsolids from aqueous solids. Aqueous solids are slurried with a lowviscosity, relatively volatile, water-immiscible light fluidizing oiland the mixture subjected to dehydration by heat evaporation wherebysubstantially all the water and part of the light fluidizing oil arevaporized. The mixed vapor is condensed and separated into a clean waterfraction and a recovered light oil fraction. The resultant slurry ofsubstantially anhydrous solids in light fluidizing oil is separated intoan oil phase and a solids phase which is laden with residual lightfluidizing oil. The separation of the oil phase and the solids phase maybe carried out as a gravity separation or a pressing apparatus of eithera static or a dynamic variety, or both, may be used. The process andapparatus of the instant invention provide for economical removal of theresidual light oil from the separated dry solids without the necessityof an extraction step.

It is therefore an object of this invention to provide process andapparatus for the dehydration of aqueous solids in a light fluidizingoil medium.

It is another object of this invention to provide process and apparatusfor the recovery of clean water from aqueous solids.

It is yet another object of this invention to provide process andapparatus for recovering substantially dry, fluidizing oil-free solidsfrom aqueous solids dehydrated in a light fluidizing oil medium.

It is still another object of this invention to provide process andapparatus for recovering essentially dry solids derived from heavyoil-containing aqueous solids which have a reduced heavy oil contentcompared to the original heavy oil content of the raw feed on amoisture-free basis.

Yet another object of this invention is to provide process and apparatusfor recovering essentially dry solids derived from heavy oil-containingaqueous solids which have substantially the same heavy oil content asthe original feed on a moisture-free basis.

The foregoing and other objects are accomplished by the practice of thisinvention. Broadly, viewed in one of its principal aspects, thisinvention consists of a process for the recovery of clean water andsubstantially dry, fluidizing oil-free solids from aqueous solidsdehydrated in a light fluidizing oil medium comprising the steps:

1. Admixing aqueous solids with a low viscosity, relatively volatilewater-immiscible light fluidizing oil to obtain a mixture which willremain fluid and pumpable after the removal of the water contenttherefrom;

2. Subjecting the resultant oil-containing mixture to dehydration byheat evaporation whereby substantially all the water and part of thelight fluidizing oil are vaporized, yielding a substantially anhydroussolids in oil slurry;

3. Condensing the resultant mixed water and light oil vapor;

4. Separating the resultant condensate into a clean water fraction and alight oil fraction;

5. Separating at least some of the relatively volatile, water-immisciblelight fluidizing oil from said substantially anhydrous solids in oilslurry, and

6. Bringing the resultant light fluidizing oil-laden solids into directcontact with blowing steam to thereby efficiently remove said light oilfrom said substantially anhydrous solids by heat evaporation.

The foregoing process is carried out in an apparatus for recoveringclean water and substantially dry, fluidizing oil-free solids fromaqueous solids dehydrated in a light fluidizing oil medium, saidapparatus comprising a systematic arrangement of items of equipment asfollows:

1. A tank adapted to receive a stream of said aqueous solids andprovided with a stirring or mixing mechanism;

2. A light fluidizing oil reservoir;

3. Means for transmitting light fluidizing oil from said light oilreservoir to said tank wherein said light fluidizing oil and aqueoussolids may be mixed;

4. An evaporator;

5. A conduit extending from said tank to said evaporator wherethroughmay flow a stream of aqueous solids admixed with light fluidizing oilfrom said tank into the evaporating region of said evaporator;

6. A condenser;

7. A conduit extending from said evaporator to said condenser throughwhich may flow a mixture of water vapor and light oil vapor formed as aresult of heating of said aqueous solids and light fluidizing oilmixture;

8. An oil-water separating means;

9. A conduit extending from said condenser to said oil-water separatingmeans wherethrough may flow a mixed condensate of water and light oil;

10. Means for separately withdrawing light oil and clean water from saidoil-water separating means;

11. A liquid-solid separating means;

12. A conduit extending from said evaporator to said liquid-solidseparating means wherethrough may flow a stream of a slurry ofsubstantially anhydrous solids in light fluidizing oil;

13. A deoiler means;

14. A conduit extending from said liquid-solid separating means to saiddeoiler means wherethrough may flow a stream of light fluidizingoil-laden solids, and

15. A combustion apparatus associated with said evaporator and saiddeoiler means for supplying evaporative heat to said evaporator andblowing steam to come into direct contact with said light fluidizingoil-laden solids in said deoiler means. The instant invention thusprovides process and apparatus for recovering solids and clean waterfrom aqueous solids dehydrated in a light fluidizing oil medium. Theinvention is characterized by the recovery not only of clean water fromaqueous solids which are dehydrated in a light oil medium but also ofresidual light oil from said solids. Aqueous solids are mixed with a lowviscosity, relatively volatile, water-immiscible light fluidizing oiland the mixture subjected to a dehydration step by heat evaporation toremove substantially all of the water and part of the light oil. Theremainder of the light fluidizing oil is then largely separated from thesolids. The light fluidizing oil-laden solids are thereafter broughtinto direct contact with steam, referred to herein as "blowing steam",in a deoiling step. Since the light oil is waterimmiscible, its directcontact with blowing steam amounts essentially to a steam distillationwherein the light oil in the presence of blowing steam boils at atemperature below its normal boiling point.

The nature and substance of the present invention as well as its objectsand advantages will be more clearly perceived and fully understood byreferring to the following description and claims taken in connectionwith the accompanying drawings which are described briefly below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the apparatus of the embodiment of the inventionwherein blowing steam is brought into direct contact with lightfluidizing oil-laden solids in a deoiler apparatus operating atessentially atmospheric pressure to thereby facilitate the removal ofsaid light oil therefrom;

FIG. 2 depicts a portion of a modified apparatus of FIG. 1 illustratingan embodiment wherein the deoiler apparatus is operated under reducedpressure;

FIG. 3 depicts a portion of a modified apparatus of FIG. 1, illustratingan embodiment wherein the aqueous solids originally contain a heavy oilwhich is extracted by the light fluidizing oil and thereafter the lightfluidizing oil and the extracted heavy oil are separated;

FIG. 4 illustrates the apparatus of that embodiment of the inventionwherein water-insoluble solids originally contain a heavy oil which isextracted by the light fluidizing oil and thereafter the lightfluidizing oil and the extracted heavy oil are separated. The lightfluidizing oil-laden water-insoluble solids are slurried with water andsaid slurry is conducted to an evaporator where at least a portion ofthe water is converted to steam, thereby directly contacting the lightoil-laden solids and facilitating the evaporation of said light oil;

FIG. 5 illustrates a portion of a modified apparatus of FIG. 1 depictingan embodiment wherein the substantially anhydrous slurry of solids inlight fluidizing oil is separated by gravity into an oil phase and aconcentrated light oil-solids slurry which is conducted to a deoilerapparatus, and

FIG. 6 depicts the apparatus of yet another embodiment of the inventionwherein the apparatus is relatively simple and compact in that a singlestage evaporator is employed and the substantially anhydrous slurry ofsolids in light fluidizing oil is separated by gravity into an oil phaseand a concentrated oil-solids slurry, thereby precluding the necessityfor a pressing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The clean water and solids recovery process of this invention as appliedto aqueous solids is thus characterized by the recovery of residuallight oil from solids previously substantially dehydrated in a lightfluidizing oil medium. The process comprises mixing aqueous solids witha low viscosity, relatively volatile, water-immiscible light fluidizingoil to obtain a mixture which will remain fluid and pumpable afterremoval of essentially its entire water content, and thereaftersubjecting the resultant mixture of solids, water and oil to adehydration step by heat evaporation whereby substantially all of thewater and at least part of the light fluidizing oil are evaporated andsubsequently recovered. Extremely dilute aqueous solids may beconcentrated by evaporation prior to mixing with the light oil. Thevapors from the subsequent oil dehydration step can be used to supplythe energy to this fluidizing oil-free concentration stage of theevaporator system. Following dehydration, the light oil is largelyseparated from the solids. Those solids carrying residual lightfluidizing oil are brought into direct contact with blowing steamwhereby the light oil is removed by heat evaporation. In one embodimentof the invention wherein the solids are water-insoluble and originallycontain heavy oil which is extracted by the light fluidizing oil, thelight fluidizing oil-laden solids are slurried with water and saidslurry is directly contacted with steam in an evaporator to therebycause evaporation of substantially all of the light oil and at leastsome of the water. The solids are then removed from the remainder of thewater as, for example, by means of a settling tank.

A critical step in the practice of the instant invention is the directcontacting of the light fluidizing oil-laden solids with blowing steamto thereby effect evaporation of said light oil. Thus, not only may theblowing steam if it be superheated supply the latent heat forevaporation of the light oil but, since said light oil and water areimmiscible and since it is a well-known scientific fact that any mixtureof two immiscible liquids must boil at a temperature lower than theboiling point of the higher boiling liquid, it follows that the lightfluidizing oil is evaporated from the solids at an appreciably lowertemperature than if the steam were merely an extraneous heat source thatdid not come into direct contact with the light fluidizing oil-ladensolids. On the other hand, the light oil-laden solids may be directlycontacted with saturated blowing steam at atmospheric pressure and atemperature of about 212° F. provided heat for vaporization of the lightoil is supplied by an external source such as via a heat jacketeddevice. Lower steam temperatures in the range of about 150° F. or lessmay be employed provided the contacting of the light oil-laden solidswith blowing steam is carried out under subatmospheric pressure andprovided heat for vaporization of the light oil is supplied by anexternal source such as by a heat jacket. It will be understood that, asa result of the external heat, the solids will in every case be at atemperature in excess of the boiling point of water at that particularpressure.

By light fluidizing oil is meant an organic liquid that iswater-immiscible and relatively fluid as well as relatively volatile.Thus, a relatively volatile fluidizing oil is mixed with the aqueoussolids prior to the dehydration thereof. Dehydration by heat evaporationresults in removal of substantially all of the water and part of thelight fluidizing oil. The remainder of the light oil is largelyseparated from the solids, thereby leaving solids laden with residuallight fluidizing oil. By the practice of this invention, light oils thatotherwise boil too high when heated by an extraneous heat source, e.g.,about 150°-550° F., can be used as the fluidizing oil in the dehydrationstep. The direct contacting of the light fluidizing oil-laden solidswith blowing steam according to this invention amounts, in effect, tosteam distillation wherein light oils that otherwise boil in the rangeof from about 150° F. to about 550° F. are distilled at temperatureswithin the range of from about 70° F. to about 400° F.

In the practice of this invention, the essentially anhydrous slurry ofsolids in light fluidizing oil is separated to recover the oil and thesolids in a largely dry condition but containing sorbed light fluidizingoil. This may be accomplished by gravity or by mechanical pressure ofeither a static or a dynamic variety, or both, on the anhydrous slurrywhereby the greater part of the oil is separated from the solids. Insome cases, as in the processing of food products, sewage sludge,rendering raw materials, or slaughter house wastes, the material itselfcontains an appreciable amount of oil independently of light fluidizingoil which may be added to it prior to the dehydration step. If this oilis a light oil, it essentially becomes part of the light fluidizing oiland will be either evaporated during dehydration and subsequentlyrecovered or carried through the dehydration step along with the solidsand the major part of the added fluidizing oil and be subjected to beingseparated from the dehydrated slurry along with the added oil. If theessentially water-free slurry be subjected to a sufficiently efficientseparation, it may thus be made to yield oil in a quantity or at a rateequal to or in excess of that in or at which oil was previously added tothe aqueous solids. If the oil associated with the aqueous solids is aheavy, relatively non-volatile oil, it may in effect be extracted fromthe essentially dry solids by the light fluidizing oil during theseparation step, e.g., a pressing operation, separated from the lightoil, and recovered. Alternatively, if the extracted heavy oil is notseparated from the light fluidizing oil and the entire oil mixture isrecycled as fluidizing oil, an equilibrium results wherein the heavy oilcontent of the essentially dry solids product is substantially the sameas that of the original feed on a moisture-free basis.

Generally it is desirable that the overall oil separation and deoilingsteps yield enough oil for reuse in the dehydration step so that theprocess will be self-sufficient with respect to light fluidizing oilrequirements. Even more desirably, in some cases such as when theaqueous solids initially contain a light oil, the combined oilseparation and deoiling steps will generate somewhat more light oil thanis needed for the dehydration step so that the process will provide anet oil yield. Also, if the aqueous solids initially contain a heavyoil, this may be extracted by the light fluidizing oil and recovered asset forth above.

No matter how vigorous the separation, e.g., pressing, of theessentially anhydrous slurry of solids in light oil, the recoveredsolids will have sorbed thereon appreciable quantities of light oilwhich, if not recovered, will be lost to the process. The liquid-solidseparating means to separate the light fluidizing oil from the solidsmay be, for example, a settling tank where separation occurs by gravity.Alternatively, separation may be by means of a mechanical press of thestatic variety, e.g., a reciprocating filter press, or, moreadvantageously, by means of a dynamic separating device such as acentrifuge. However, both static and dynamic presses may be used.Accordingly, most of the light oil is pressed from the solids in, forexample, a centrifuge, and the oil may be collected in a suitablereservoir where it is available for reuse in the process if so desired.If the aqueous solids originally contain a heavy oil, it may beseparated from the essentially anhydrous solids due to extraction by thelight fluidizing oil during the liquid-solid separating step. If theseparate oil is divided into its light oil and heavy oil components andonly the light oil component recycled as fluidizing oil, the net resultis a reduction in the heavy oil content of the dry solids. On the otherhand, if the gross separated oil comprised of light fluidizing oil andextracted heavy oil is recycled as the fluidizing oil, an equilibrium isattained wherein heavy oil is put back into the dry solids at the samerate it is removed by the recycled gross fluidizing oil. The net resultis essentially dry solids having substantially the same heavy oilcontent on a moisture-free basis as the original feed.

Since the light fluidizing oil may have a low viscosity and a lowspecific gravity, e.g., light oils of petroleum origin, the dehydratedslurry from the evaporator can be transferred to a settling tank wherebya more concentrated solids in oil phase may be separated as a thickenedslurry; the bulk of the oil remains at the stop of the tank from whichit may be recycled to the process. The foregoing gravity separationoperation does not require a mechanical press of either a static or adynamic variety.

The concentrated oil-solids slurry or solids having oil sorbed thereonare then brought into direct contact with blowing steam. The blowingsteam, if superheated, supplies latent heat for the evaporation of thelight oil or, alternatively, saturated blowing steam at about 212° F.may be used in conjunction with external heat as from a steam jacket tosupply heat for evaporation of the light oil. Since the light oil iswater-immiscible, its direct contact with the blowing steam amountsessentially to a steam distillation wherein the light oil boils at atemperature below its normal boiling point. Thus, not only is the lightoil more readily evaporated from the solids with less heat energy beingrequired from the blowing steam alone or in conjunction with anextraneous heat source such as indirect thermal contact with steam oranother heat transfer fluid in, for example, a steam jacket, but itmakes possible the use of higher boiling light oils. Any heavy oilpresent on the dry solids, however, is essentially not evaporated.

The direct contacting of oil-laden solids or a concentrated oil-solidsslurry with blowing steam, as discussed above, permits evaporation ofthe light oil at a temperature below its normal boiling point. However,in certain applications such as deoiling of temperature-sensitivematerials like food products for human consumption and animal feeds,even lower temperatures for evaporation of the light oil are desired.This may be accomplished by contacting the oil-laden solids with blowingsteam at less than atmospheric pressure.

The removal of light oil from the solids by direct contact with blowingsteam may conveniently take place in a deoiler apparatus which mayadvantageously be connected to the discharge of the settling tank orpressing apparatus, e.g., a centrifuge, and which may be operated atatmospheric or less than atmospheric pressure. If desired, the deoilerapparatus may be externally heated as by means of a steam jacket.Blowing steam is passed into the deoiler apparatus containing theconcentrated oil-solids slurry or oil-laden solids. It is desirable toutilize effluent blowing steam and vaporized light oil from the deoilerapparatus in the process as a source of heat. The vaporized light oil iseventually condensed and reused in the dehydration process. Any heavyoil present on the solids is essentially not evaporated.

In one embodiment of the invention, the aqueous solids arewater-insoluble and are intially associated with a heavy oil which issubstantially extracted by the light fluidizing oil, and thereafter thelight fluidizing oil and the extracted heavy oil are separated. Thelight fluidizing oil-laden solids are slurried with water and the slurryconducted to the evaporating region of an evaporator where at least aportion of the water is converted to steam. That steam is the blowingsteam which directly contacts the light oil-laden solids and causesevaporation of the waterimmiscible light oil in the same general way asthe evaporation occurs in the deoiler apparatus described above. Asmentioned, some water of the aqueous slurry is also evaporated. Thesolids are then separated from the remaining water by such means as afilter or a settling tank. The recovered solids are not only free oflight fluidizing oil, but they are also essentially free of the heavyoil with which they were originally associated.

The solids left after removal of the light oil therefrom by directcontact with blowing steam may often be utilized for purposes outsidethe process itself and thus constitute a process product. The processand apparatus of this invention may be used to recover clean water andessentially dry solids from aqueous solids derived from numerous sourceswhether they be waste solids or solids having intrinsic value. Thus, forexample, this invention finds utility in the recovery of water andsolids from a variety of materials which are found in aqueous solution,in water dispersion or otherwise associated with water, e.g., powderedcoal, food products, animal feeds and wastes, cement, spent lime,inorganic salts, sewage, sewage sludge, slaughter house effluent andrendering materials, slimes, black liquors from the paper industry,certain tree barks, the organic streams from garbage disposal plants,pharmaceutical products and wastes, cannery or canning factory effluent,chemicals, etc. Accordingly, depending on the source, the solidsrecovered from the blowing steam contacting operation may be used asfertilizer, as animal feed, or possibly as food for human consumption,e.g., a dehydrated, fat-free food product. Further, since they are oftenburnable, they may be used as fuel for the generation of steam needed torun the evaporator component of the apparatus, blowing steam forcontacting the concentrated oil-solids slurry or the oil-laden solids,and also the steam needed to run auxiliary equipment such as pumps,either directly if they be steam-driven pumps or indirectly if they bemotor driven punps and the steam is used to run a turbogeneratordirectly. Any heavy oil remaining on the essentially dry solids also mayhave fuel value. The process may thus be at least partly self sufficientin respect of fuel requirements. The process and apparatus of thisinvention thus provide means for the recovery of essentially clean waterand valuable solid products from aqueous solids. Furthermore, thisinvention is characterized by the fact that residual light fluidizingoil from the dehydration step that is sorbed on or otherwise associatedwith the solids is efficiently recovered for reuse.

The material to be treated by the process of this invention shouldcontain solid particles generally smaller than about 1/4 inch. However,larger particles are acceptable, as in the case of bone for gelatinmanufacture, provided that the clearances between heat transfer surfacesis increased accordingly. Larger particles may be ground to size orcomminuted by existing techniques.

The light oils that are utilized for admixture with the aqueous solidsprior to the dehydration operation are inert and waterimmiscible. Inaddition, they should be sufficiently volatile to be evaporated bydirect contact with blowing steam at a temperature within the range offrom about 70° F. to about 400° F. Generally, light oils boiling withinthe range of from about 150° F. to about 550° F., and preferably fromabout 300° F. to about 450° F., are contemplated as being useful forthis purpose. Light oils such as hydrocarbon oils boiling within therange of about 325° F. to about 400° F. are particularly preferred inthe processing of animal feeds and food products for human consumptionsince this boiling range permits almost complete removal of the oil fromthe dried solids product. The usually preferred class of ligh oil islight hydrocarbon oil. The light hydrocarbon oil may be normalparaffinic, isoparaffinic, aromatic, or naphthenic. Examples of suitablelight hydrocarbon oils are n-pentane, isopentane, n-hexane, cyclohexane,benzene, isooctane, eicosane, petroleum fractions boiling in the rangeof from about 300° F. to about 450° F., isohexane, xylene, octadecane,toluene, n-heptane, cyclopentane, and mixtures thereof. Another class ofsuitable light oils is water-immiscible fatty alcohols. Examples ofsuitable alcohols are n-hexyl alcohol, n-heptyl alcohol, isoheptylalcohol, n-octyl alcohol, isooctyl alcohol, n-nonyl alcohol, and n-decylalcohol. Fatty acids such as caproic acid and capric acid may also beused as the light oil. In processing food products and animal feed, anFDA approved light oil such as the series of isoparaffinic oilsmanufactured by Humble Oil and Refining Company under the trademark"Isopar" may be used. Particularly preferred in processing animal feedsand food products for human consumption is Isopar H because its flashpoint permits safe operation and its boiling temperature, which iswithin the range of about 325° F. to 400° F., allows for almost completeremoval of the oil from the dried food product, thereby complying withFDA regulations. Generally, materials that are liquid at the temperatureof operation, that are preferably oil-like and that are relativelyvolatile and essentially immiscible with water may be employed. It isoften desirable to employ a light oil that imparts process credits,i.e., one that can add value to the solids product, such as waste oilsnormally found in sewage or industrial waste, or fuel oils, or, assuggested above, employ oils derived in the practice of the processitself so as to minimize cost factors. The quantity of light fluidizingoil is such that its ratio in the system is in the range of about 2 toabout 20 parts or more by weight, based on each part of non-fat ornon-oil based solids. This refers to total oil, i.e., that added plusthat derived from the process for reuse. This amount of oil gives afluid, pumpable mixture even in the absence of water. The term "fluid"as used here is intended to be synonomous with "liquid," i.e., takingthe shape of the container to the extent that the mixture fills thecontainer.

While the dehydration step of this invention may be carried out in thesingle stage or single effect evaporators known in the art, it ispreferred that this step be accomplished in a plurality of sequentialheat evaporation steps wherein each of the successive evaporation stepsis at a successively higher temperature and the resulting solids streamsare of successively higher concentration because of increasingdehydration, the evolved vapors of each evaporation step supplying asubstantial portion of the heat requirements of the preceding heatevaporation step. Thus the plurality of sequential heat evaporationsteps connotes at least two. The temperatures, pressures andconcentrations in each of the successive series of evaporation steps arelargely empiric in nature, depending upon the systems and oils beingemployed. The normal processing temperatures for the dehydration of thelight fluidizing oil-aqueous solids mixture may be in the range of about70° F. to about 250° F. in the first stage and in the range of about100° F. to about 400° F. in the second, third or final stages of amulti-effect drying system. The preferred processing temperatures are inthe range of about 90° F. to about 175° F. in the first stage and in therange of about 125° F. to about 350° F. in the second, third or laststages. The foregoing ranges and progressions of temperatures arereasonable in the case where the flows through the evaporator of themixture being dehydrated and the heating or drying steam aresubstantially countercurrent, the evaporator in that mode of operationbeing called a "backward flow" evaporator. The temperatures also dependon the desired quality of the end product and the economics of fuelutilization, cooling water availability, capital investment, etc.

In the foregoing paragraph the expression "first stage" refers to thatpart of the evaporator equipment in which the light fluidizingoil-aqueous solids mixture is subjected to the first step of asequential plurality of evaporation steps, two or three or morecorresponding to "second stage," "third stage," etc. The expression"effect," on the other hand, as in "multiple-effect" or "multi-effect,"is related to the flow and action of the heating medium, customarilysteam, in the evaporator equipment. Where the flow of a light fluidizingoil-aqueous solids mixture being heated and evaporated is countercurrentto that of the heating steam (backward flow), the first stage of theevaporator is the same as its last effect.

The pressures are not critical and are controlled with temperatures toachieve desired evaporation rates in a given design. Thus the firststage pressure will conveniently be from about 1/2 inch Hg absolute toapproximately atmospheric. The pressures then increase in successivestages responsive to the temperatures in the aforedescribedcountercurrent or backward flow case. It is advantageous to operate thefirst stage at subatmospheric pressures and the final stages at close toatmospheric.

The advantage of the sequential evaporation steps may be seen from thefollowing. For example, in a double-effect evaporator with feed enteringat 80° F., the material can leave the evaporator at 225° F.-250° F. withratios of approximately one pound of steam utilized for approximately1.5 to 1.75 pounds of water evaporated; whereas in normal single-effectoperations about 1.5 pounds of steam could be required to achieve thesame result with only one pound of water evaporated. If triple or moreeffect evaporation be utilized, even further economies in fuelconsumption are made possible. It should be noted that the evolvedvapors from each of the heat evaporation steps after the first stepsupply a substantial portion of the heat requirements of the precedingheat evaporation step or stage in the case of a backward flowevaporator. The only net or external heat input required is that neededto raise the temperature of the components to evaporation temperaturesand to provide heat of vaporization as well as to make good for heatlosses. The final product from the dehydration step is generally asubstantially anhydrous oil-solids slurry containing no more than about5-10 weight percent water on a non-fat basis.

Although backward flow evaporators are preferred, any type may be used.Thus, backward flow evaporators, forward flow evaporators, forwardflow-backward flow evaporator combinations or, indeed, any combinationthereof may be used. The equipments that are generally preferred aremultiple-effect evaporators known in the art, e.g., Mojonnier,Bufflovac, Rodney-Hunt, recompression type evaporators such as thermalor mechanical recompression types, etc. Functionally, evaporatorequipment may be of the forced circulation, flash, falling filmrecirculation, single pass, rotary wiped film, plate, or indeed anysuitable type.

The separation of solids from the light fluidizing oil can beconveniently carried out by gravity separation or in a liquid-solidsseparating means, preferably in a dynamic press such as a centrifuge.The concentrated oil-solids slurry or solids having residual light oilsorbed thereon which are recovered from the liqud-solid separatingmeans, e.g., centrifuge, are then brought into direct contact withblowing steam for removal of the residual light oil therefrom. Anyresidual heavy oil that may be present on the solids is essentially notremoved by contact with the steam. In the embodiment of the inventionexemplified in FIG. 1, oil-laden solids exiting from the centrifugeenter a deoiler apparatus operating at essentially atmospheric pressurewhere they are brought into direct contact with blowing steam. Thedeoiler apparatus may advantageously be externally heated as by passingsteam through a heating jacket surrounding it. The blowing steam ispreferably saturated steam at close to 212° F. and atmospheric pressure,but it may also be superheated in the range of about 250° F. to 500° F.The blowing steam coming in contact with light oil-laden solids withinthe deoiler apparatus causes evaporation of the light oil at atemperature below its normal boiling point. As stated above, anyresidual heavy oil on the oil-laden solids is not appreciablyevaporated. The vaporized light oil and effluent blowing steam mayadvantageously be conducted from the deoiler apparatus and the energythereof recovered as useful work as, for example, by being used as asource of heat in the evaporator region of the system.

In the embodiment depicted in FIG. 2, the deoiler apparatus is connecteddirectly to a drying evaporator operating under reduced, or less thanatmospheric, pressure. As a result, the deoiler apparatus is also underreduced pressure. Hence, the deoiling operation requires less blowingsteam and may be carried out at reduced temperature, an advantage whendeoiling a temperature-sensitive material such as a food product forhuman consumption or an animal feed. The deoiler apparatus may beexternally heated, as by a steam jacket, to provide latent heat.

In the embodiment depicted in FIG. 3, the aqueous solids originallycontain a heavy oil which is extracted by the light fluidizing oil andthereafter the light fluidizing oil and the extracted heavy oil areseparated. The light fluidizing oil is recycled through the system. Theoil-laden solids, as in FIG. 1 of which FIG. 3 is a modification, aredirectly contacted with blowing steam in a deoiler apparatus for removalof residual light fluidizing oil therefrom. Extraction of heavy oilinitially in association with the aqueous solids by the light fluidizingoil results in a net decrease in the heavy oil content of the resultantessentially dry solids.

In the embodiment illustrated in FIG. 4, the aqueous solids arewater-insoluble and originally contain a heavy oil which is extracted bythe light fluidizing oil. The light fluidizing oil and the extractedheavy oil are separated and the light oil recycled through the system.The light oil-laden solids are slurried with water in a repulping tank.The water slurry is conducted to the evaporating region of an evaporatorwhere at least a portion of the water is converted to steam whichdirectly contacts the slurry and causes evaporation of the light oil andpart of the water. The solids are then separated from the water. Sinceheavy oil initially associated with the aqueous solids is extracted bythe light fluidizing oil, the net result is a substantial decrease inthe heavy oil content of the recovered solids.

In the embodiment exemplified in FIG. 5, the substantially anhydrousslurry of solids in light fluidizing oil is separated by gravity in asettling tank into an oil phase and a concentrated light oil-solidsslurry. The separated oil is removed from the top of the settling tankand recycled through the system. The concentrated light oil-solidsslurry is pumped to a deoiler apparatus where it is brought into directcontact with blowing steam which causes evaporation of the light oil ata temperature below its normal boiling point. While the deoilerapparatus depicted in FIG. 5 is operating at essentially atmosphericpressure, it will be understood that it may alternatively be operatedunder reduced pressure.

In the embodiment depicted in FIG. 6, the apparatus is relatively simpleand compact in that a single stage evaporator is used and thesubstantially anhydrous slurry of solids in light fluidizing oil isseparated by gravity into a light oil phase and a concentrated lightoil-solids slurry, thus making a pressing apparatus unnecessary. Theseparated light oil is recycled through the system while theconcentrated light oil-solids slurry is pumped to a deoiler apparatus.Effluent blowing steam and vaporized light oil from the deoilerapparatus are conducted directly to the single stage evaporator of thesystem to supply evaporative heat thereto. In view of the single stageevaporator employed, such use of the effluent blowing steam andvaporized light oil from the deoiler apparatus is essential in order toachieve efficient steam utilization in the system.

This invention will be most clearly perceived and best understoodthrough reference to the preferred embodiments as discussed in furtherdetail in connection with the flow diagrams shown in the drawings. Inthe embodiment illustrated in FIG. 1, a stream of aqueous solids insolution or dispersion enters fluidizing tank 10 through line 12. Lightfluidizing oil enters fluidizing tank 10 through line 14. The fluidmixture in fluidizing tank 10 is agitated by means of stirring device 16and then withdrawn from the fluidizing tank by means of pump 18. Pump 18delivers the mixture through line 20 to the evaporating region of thefirst stage or third effect evaporator 22 of an overall dryingevaporator assembly or array. In evaporator 22 water and a portion ofthe light oil are boiled off at a subatmospheric pressure which maytypically be about 2 to 10 inches Hg absolute. The temperature of thepartially dehydrated and partially deoiled product of the enteringmixture of aqueous solids in light oil is in the range of about 70°-250°F. and preferably about 90°-175° F., depending on the pressure in theevaporator. The system is heated by mixed steam and light oil vapor fromline 24 which is at a temperature about 30°-40° F. higher than thetemperature of the partially dehydrated aqueous solids in oil mixtureand which comes from the vapor chamber of the succeeding or second stageof the evaporator. Condensate of the heating vapor is withdrawn throughline 26 which meets line 28 at a "T" joint or connection. The condensateis conducted through line 28 to oil-water separator 30. Mixedsteam-light oil vapor formed as a result of the partial dehydration ofthe entering mixture of aqueous solids in light oil is removed from thevapor chamber of evaporator 22 through line 34 into surface condenser 36within which a partial vacuum is maintained by means of vacuum pump 38which is connected to surface condenser 36 via vacuum line 40.

The mixture of water and light oil vapors entering surface condenser 36through line 34 is condensed by cooling water entering the condenserthrough line 42 and leaving the condenser through line 44. The mixedcondensate of warm water and light oil is discharged from the condenserthrough line 46 into oil-water separator 30.

Inside oil-water separator 30, the mixture of water and light oil isseparated into light oil and partially clarified water containing somelight oil. The separated light oil is removed from oil-water separator30 through line 48 and is conducted thereby to light oil storage tank50.

The partially clarified water is conducted from oil-water separator 30via line 54 to coalescer 56. Inside coalescer 56, the partiallyclarified water containing some light oil is separated into light oiland clean product water. The separated light oil is withdrawn fromcoalescer 56 through line 58, which meets line 48 at a "T" joint, and isultimately conducted to light oil storage tank 50. Clean product wateris withdrawn from coalescer 56 through line 60. If desired, part of theproduct water may be reused throughout the system. Alternatively, allthe recovered water may be stored in a reservoir for later use inapplications in which essentially clean water is required.

The partially dehydrated mixture of aqueous solids in light oil fromevaporator 22 is continuously removed through line 62 with theassistance of pump 64. The partially dehydrated mixture is forcedthrough line 62 to the evaporating region of second stage 66 of theevaporator. In the second stage evaporator a procedure is followed whichis similar to that in the first stage except that the pressure ishigher. The pressure in each succeeding evaporator stage is somewhathigher than in the preceding stage, approaching approximatelyatmospheric pressure in the last stage. The temperature of the furtherdehydrated product of the second stage evaporator is in the range ofabout 100°-400° F. and preferably about 125°-350° F., depending on thepressure in the evaporator. The heating medium is mixed steam and lightoil vapor which is at a temperature about 30°-40° F. higher than thetemperature of the further dehydrated aqueous solids slurry leaving thesecond stage evaporator. The mixed heating vapor comes through line 68from the vapor chamber of the third or succeeding evaporator stage.Condensate of the mixed heating vapor is withdrawn from second stageevaporator 66 through line 28 and is discharged into oil-water separator30. As mentioned above, mixed steam-light oil vapor formed as a resultof the furher dehydration of the partially dehydrated mixture of aqueoussolids in light oil is removed from the vapor chamber of second stageevaporator 66 through line 24 and is used as the heating medium in firststage evaporator 22.

The further dehydrated slurry of aqueous solids in light oil withdrawnfrom second stage evaporator 66 is discharged by pump 70 through line74. The further dehydrated mixture is conducted through line 74 to theevaporating region of third stage 76 of the evaporator. The pressure inthe third stage is higher than in the second stage, advantageously beingapproximately atmospheric. The temperataure of the product of thirdstage evaporator 76, i.e., a slurry of solids in light oil containingabout 1% by weight of water based on the entire slurry, is greater thanthat of second stage evaporator 66 and is within the range of about100°-400° F. and preferably about 150°-350° F. The heating medium forthird stage evaporator 76 is steam at a temperature about 30°-50° F.higher than that of the product, i.e., an essentially anhydrous slurryof solids in light oil. This steam is generated in boiler-furnace 77 andconveyed to third stage 76 of the evaporator through line 78. Condensateof the heating steam is withdrawn through line 80 and returned to theboiler-furnace. As already mentioned, mixed steam-light oil vapor formedas a result of the still further dehydration of the slurry of solids inlight oil is removed from the vapor chamber of third stage evaporator 76through line 68 and is used as the heating medium in second stageevaporator 66.

The essentially anhydrous slurry of solids in light oil is withdrawnfrom third stage evaporator 76 and is forced by pump 82 through line 84to continuous centrifuge 86. The light oil is separated from the solidsin centrifuge 86 and is conducted therefrom via line 88 to light oilstorage tank 50. Recovered light fluidizing oil is discharged by pump 90through line 14 to fluidizing tank 10 for recycling through the system.If the process provides a net yield of oil, it may be recovered fromtank 50 and stored for use outside the system.

The solids, having residual light oil sorbed thereon, exit fromcontinuous centrifuge 86 and enter live bottom bin 94 via conduit 96.The live bottom of bin 94 causes the solids to advance to the exitthereof where they are conducted by gravity through conduit 98 into cakedeoiler apparatus 100. Deoiler apparatus 100 may, if desired, beexternally heated by steam generated in boiler-furnace 77 which enterssteam jacket 102 through line 104. Condensate of the jacket steam iswithdrawn through line 106 and returned to the boiler-furnace. Blowingsteam generated in boiler-furnace 77 is conducted via line 104 to line108, which is connected thereto by a "T" joint, and from line 108 intodeoiler apparatus 100 where said steam comes into direct contact withthe light oil-laden solids and causes vaporization of said light oil ata temperature below its normal boiling point. Effluent blowing steam andvaporized light oil exit from the deoiler apparatus through line 110.

The solids, free from sorbed light oil, are discharged by gravity fromdeoiler apparatus 100 through conduit 114 into live bottom bin 116. Thescrew conveyor bottom of bin 116 conducts the solids to the exit thereofwhere said solids, free from the fluidizing light oil as well as beingin an essentially anhydrous state, are discharged through line 118 intogrinder or comminutor 119. By means of grinder 119 the solids arereduced to granular if not powder form, and from the grinder they flowthrough line 120 to a rotary selector valve 121 by which they may bedirected to either line 122 or line 123. Line 122 leads to collecting orbagging equipment, and through it the solids may be withdrawn for useoutside the illustrated system. Line 123, shown as active according tothe setting of valve 121, leads to the suction of blower 124, and thisblower discharges the comminuted solids to the combustion region ofboiler-furnace 77 through line 125.

Effluent blowing steam and vaporized light oil exiting from deoilerapparatus 100 are conducted by line 110 to second stage evaporator 66where the mixed vapor supplies evaporative heat to said second stageevaporator. Since the second evaporator stage is operated at less thanatmospheric pressure, a valve 126 which is equipped with a pressuresensor is located on line 110 and serves to maintain slightly less thanatmospheric pressure in deoiler apparatus 100. The deoiling step istherefor conducted at essentially atmospheric pressure. Thus, in theembodiment shown, the energies of effluent blowing steam and thevaporized light oil are recovered constructively by supplying heat tosecond stage evaporator 66. Condensate of the heating steam andvaporized light oil is withdrawn from the second stage evaporatorthrough line 28 and discharged into oil-water separator 30. While theeffluent blowing steam and the vaporized light oil from deoilerapparatus 100 are depicted in FIG. 1 as supplying evaporative heat tosecond stage evaporator 66, it will be understood that the energy of themixed vapors may be recovered by supplying heat to first stageevaporator 22 or, indeed, to any evaporating stage in the system exceptto the shellside of third stage evaporator 76 since the oil containedtherein would contaminate the condensate returned to boiler-furnace 77through line 80 and also since the temperature of the vapors may not besufficiently high to provide for the heat transfer requirements.Alternatively, the effluent blowing steam and vaporized light oil may beused for preheating the aqueous solids-light fluidizing oil mixture byinjection into fluidizing tank 10 or, indeed, at any other location inthe system where recovery of its energy can offer process credits.

The foregoing description of FIG. 1 applies to the case where theaqueous solids do not initially contain a heavy, relatively non-volatileoil. If there had been a heavy, relatively non-volatile oil originallyassociated with the aqueous solids, the heavy oil would have beenextracted by the light fluidizing oil during the pressing operation. Inthe embodiment depicted in FIG. 1, the entire oil fraction from thepressing operation is recycled as fluidizing oil. Accordingly, if aheavy oil were present an equilibrium would soon be attained whereinheavy oil was extracted from the aqueous solids by the fluidizing oil atthe same rate it was replaced by the recycled oil. The net result wouldbe an essentially dry solids product having substantially the same heavyoil content as that of the original feed on a moisture-free basis.

FIG. 2 depicts a portion of the apparatus used in a modification of theapparatus of FIG. 1 wherein the deoiler apparatus is directly connectedto a drying evaporator operating under reduced pressure. Accordingly,the deoiler apparatus is also under reduced pressure. The apparatus ofFIG. 2 differs primarily from that of FIG. 1 in that line 110 does notcontain a valve 126 equipped with a pressure sensor, and there is afirst rotary valve or its equivalent on conduit 98 between live bottombin 94 and deoiler apparatus 100 and a second rotary valve or itsequivalent on conduit 114 between deoiler apparatus 100 and live bottombin 116. The advantages of operating the deoiler apparatus under reducedpressure are that the deoiling process requires less blowing steam, andit may be carried out at lower temperatures which is advantageous whendeoiling a temperature-sensitive material such as a food product oranimal feed.

In FIG. 2 light oil-laden solids discharged from continuous centrifuge86 via conduit 96 enter live bottom bin 94. The live bottom of bin 94causes the solids to advance to the exit thereof where they enterconduit 98 and are conveyed by rotary valve 127 into deoiler apparatus100. As in FIG. 1 deoiler apparatus 100 may, if desired, be externallyheated by steam which enters steam jacket 102 through line 104.Condensate of the jacket steam is withdrawn through line 106. Blowingsteam generated in a boiler-furnace enters deoiler apparatus 100 vialine 108 and comes into direct contact with the light oil-laden solids,thus causing vaporization of said light oil. The solids, free fromresidual light oil, are discharged from deoiler apparatus 100 viaconduit 114 and are urged by means of rotary valve 128 into live bottombin 116. The solids, free from fluidizing light oil as well as beingessentially dry, are finally discharged from live bottom bin 116 viaconduit 118. However, as described above in connection with FIG. 1, ifthe aqueous solids initially contained a heavy oil, the essentially drysolids product would contain heavy oil in an amount substantially thesame as that of the original feed on a moisture-free basis.

Effluent blowing steam and vaporized light oil exit from deoilerapparatus 100 through line 110. Line 110 is connected to an evaporatorstage operating under reduced pressure whereby the energy of theeffluent blowing steam and the vaporized light oil is recoveredconstructively by supplying heat to said evaporator stage. Because, asmentioned above, there is no valve equipped with a pressure sensor online 110, deoiler apparatus 100 is in direct connection with theevaporator stage operating under reduced pressure. Since rotary valves127 and 128 are essentially air tight, deoiler apparatus 100 is as aresult under reduced pressure even though live bottom bins 94 and 116 towhich it is connected are under essentially atmospheric pressure.

FIG. 3 depicts a portion of a modified apparatus of FIG. 1 wherein theaqueous solids originally contain a heavy oil which is extractedtherefrom by the light fluidizing oil during the liquid-solid separatingstep. The light fluidizing oil and the extracted heavy oil are thenseparated and the light component recycled as fluidizing oil. The netresult is a reduction in the heavy oil content of the essentially drysolids product. For example, if the aqueous solids are products of therendering industry which commonly contain about 10-15 weight percent ofheavy oils and fats such as tallow and other animal fats, extraction bythe light fluidizing oil yields a product containing only about 6-7weight percent of such heavy oils and fats. Another example of aqueoussolids containing heavy oils and fats is the bark of such trees as fir,spruce, ash and southern pine. Dehydration by the method illustrated inFIG. 3 results in the recovery from the bark of a valuable wax similarto carnauba wax. Yet another example of aqueous solids containing heavyoils is the organic stream from garbage disposal plants. This materialtypically contains about 5 weight percent of heavy oils in the form of,among other things, polyethylene and polyvinylchloride. Recovery ofthese polymeric materials makes them available for recycling.Additionally, removal of polyvinylchloride from the dried sludge meansthat the sludge may be burned without evolution of corrosive hydrogenchloride.

In FIG. 3 a mixture of light fluidizing oil and heavy oil extracted fromthe solids by the light oil is conducted from centrifuge 86 via line 88to light-heavy oil storage tank 130. Light oil-laden solids having areduced heavy oil content compared to the original heavy oil content ofthe raw feed on a moisture-free basis are discharged from centrifuge 86through conduit 96 and thereafter treated according to either of theprocedures described above in connection with FIG. 1 and FIG. 2.

The mixture of light and heavy oils is withdrawn from tank 130 andforced through line 132 by pump 134 which is located thereon. Steam isintroduced into line 132 through line 136 which joins line 132 at a "T"joint. The mixture of light and heavy oils and live steam is conductedthrough line 132 to stripping evaporator 138. Indirect steam to supplylatent heat for the evaporation of the light oil fraction is conductedfrom a boiler-furnace to stripping evaporator 138 via line 140.Condensate of the indirect steam is returned to the boiler-furnace fromstripping evaporator 138 through line 146. The light oil is vaporized instripping evaporator 138. Light oil vapor mixed with the direct steamintroduced through line 136 is conducted from the vapor chamber ofevaporator 138 via vapor duct 148 which is joined to line 68 at a "T"joint. As discussed above, line 68 conducts a mixed steam-light oilvapor from third stage evaporator 76 to second stage evaporator 66 tosupply evaporative heat thereto. The mixed light oil and water vapors invapor duct 148 are therefore conducted into line 68 and the combinedmixed vapors are used as the source of evaporative heat in second stageevaporator 66.

The extracted heavy oil, which is not vaporized in evaporated 138, iswithdrawn from stripping evaporator 138 and forced through line 150 bypump 152 which is located thereon. The heavy oil is conducted via line150 to heavy oil storage tank 154. The heavy oil can be utilized forfuel or other marketing values depending on the composition of theoriginal aqueous solids feed and whether these materials are useful foranimal feed, food for human consumption, or non-food purposes.

As mentioned above in the discussion of FIG. 1, condensate of the mixedheating vapor is withdrawn from second stage evaporator 66 through line28 and conducted to oil-water separator 30. Inside oil-water separator30 the mixture is separated into a light oil fraction and partiallyclarified water containing some light oil. The separated light oil isconducted from oil-water separator 30 via line 48 to light oil recycletank 156. The partially clarified water is removed from oil-waterseparator 30 via line 54 and conducted to coalescer 56 where it isseparated into light oil and clean water product. The separated lightoil is withdrawn from coalescer 56 through line 58, which meets line 48at a "T" joint, and is ultimately conducted to light oil recycle tank156.

Light oil is removed from light oil recycle tank 156 by pump 158 andforced through line 160 to fluidizing tank 10. Since the light oil isseparated from the extracted heavy oil prior to being recycled tofluidizing tank 10 an equilibrium is not attained, and the net result isthe extraction of heavy oil from the solids by light fluidizing oil incentrifuge 86. The extraction of the heavy oil thus reduces the finaloil content of the essentially dry solids product, thereby oftenenhancing the commercial value of the solids for fertilizer, animalfeed, food for human consumption and other uses.

It will be understood by those skilled in the art that the modificationof FIG. 1 depicted in FIG. 3 is equally applicable to FIG. 2 in caseswhere the aqueous solids feed is initially associated with a heavy oil.In each case an essentially dry solids product having a reduced heavyoil content is obtained.

FIG. 4 depicts the flow diagram of the apparatus of that embodiment ofthe invention wherein water-insoluble solids originally contain a heavyoil which is extracted by the light fluidizing oil and thereafter thelight fluidizing oil and the extracted heavy oil are separated. Thelight fluidizing oil-laden water-insoluble solids are slurried withwater and said slurry is conducted to an evaporator where at least aportion of the water is converted to steam, thereby directly contactingthe aqueous slurry of light oil-laden solids and facilitating theevaporation of said light oil.

In the embodiment of the process employing the apparatus depicted inFIG. 4, a stream of water-insoluble solids associated with a heavy oiland in aqueous dispersion enters fluidizing tank 164 through line 166.Light fluidizing oil enters fluidizing tank 164 through line 168. Theliquid mixture in fluidizing tank 164 is agitated by means of stirringdevice 170 and then withdrawn from the fluidizing tank by means of pump174. Pump 174 delivers the mixture through line 176 to the evaporatingregion of second stage evaporator 178 of an overall three-stageevaporator assembly or array. In evaporator 178 water and a portion ofthe light oil are boiled off at a pressure which may typically bebetween about 2 to 10 inches Hg absolute and about atmospheric. Thetemperature of the partially dehydrated and partially deoiled product ofthe entering mixture of aqueous solids in light fluidizing oil is in therange of about 100°-400° F. and preferably about 125°-350° F., dependingon the pressure in the evaporator. The system is heated by mixed steamand light oil vapor from line or vapor duct 180 which is at atemperature about 30°-40° F. higher than the temperature of thepartially dehydrated aqueous solids in oil mixture, and which comes fromthe vapor chamber of the succeeding or third stage of the evaporator.Condensate of the heating vapor is withdrawn through line 182 whichmeets line 184 at a "T" joint. The mixed condensate is conducted throughline 184 to oil-water separator 186. Mixed steam-light oil vapor formedas a result of the partial dehydration of the entering mixture ofaqueous solids in light oil is removed from the vapor chamber ofevaporator 178 through line 188 to first stage evaporator 190 where themixed vapors serve as the source of heat for said first stageevaporator. Condensate of the mixed heating vapors is withdrawn fromevaporator 190 through line 192, which meets line 184 at a "T" joint,and ultimately through line 184 to oil-water separator 186.

The partially dehydrated mixture of aqueous solids in oil fromevaporator 178 is continuously removed through line 194 with theassistance of pump 196. The partially dehydrated mixture is forcedthrough line 194 to the evaporating region of third stage or firsteffect 198 of the evaporator assembly. In the third stage evaporator aprocedure is followed which is similar to that in the second stageexcept that the pressure is higher. The pressure in each succeedingevaporator stage is usually somewhat higher than in the preceding stage,approaching approximately atmospheric pressure in the third and laststage. The temperature of the product of third stage evaporator 198,i.e., a slurry of solids in light fluidizing oil plus heavy oiloriginally associated with the solids and containing about 1% by weightof water based on the entire slurry, is greater than that of the productof second stage evaporator 178 and is within the range of about100°-400° F. and preferably about 150°-350° F. The heating medium issteam at a temperature about 30°-50° F. higher than that of the product,i.e., an essentially completely dehydrated slurry of solids in oil. Thissteam is generated in boiler-furnace 200 and conveyed to third stage 198of the evaporator through line 204. Condensate of the heating steam iswithdrawn through line 206 and returned to boiler-furnace 200.

The essentially anhydrous slurry of solids in oil is withdrawn fromthird stage evaporator 198 and is discharged by pump 208 through line210. The slurry is forced through line 210 to continuous centrifuge 212.The light fluidizing oil and extracted heavy oil are separated from thesolids in centrifuge 212 and conducted therefrom through line 214 tolight-heavy oil tank 216.

The mixture of light and heavy oils is withdrawn from tank 216 andforced through line 218 by pump 220 which is located thereon. Steam isintroduced into line 218 through line 222 which joins line 218 at a "T"joint. The mixture of light and heavy oils and live steam is conductedthrough line 218 to stripping evaporator 224. Indirect steam to supplylatent heat for the evaporation of the light oil fraction is conductedfrom a boiler-furnace to stripping evaporator 224 via line 226.Condensate of the indirect steam is returned to the boiler-furnace fromstripping evaporator 224 through line 228. The light oil is vaporized instripping evaporator 224. Vaporized light oil and the direct steamintroduced through line 222 are conducted from the vapor chamber ofevaporator 224 via vapor duct 230 which is joined to vapor duct 180 at a"T" joint. As discussed above, vapor duct 180 conducts a mixedsteam-light oil vapor from third stage evaporator 198 to second stageevaporator 178 to supply evaporative heat thereto. The mixed light oilvapor and steam in vapor duct 230 are therefore conducted into line 180and the combined mixed vapor is used as the source of evaporative heatin second stage evaporator 178.

The extracted heavy oil, which is not vaporized in stripping evaporator224, is withdrawn therefrom and forced through line 234 by pump 236which is located thereon. The heavy oil is conducted through line 234 toheavy oil storage tank 238. The heavy oil can be utilized for fuel orother purposes depending on the composition of the original aqueoussolids feed.

The water-insoluble solids having residual light oil sorbed thereon aredischarged from centrifuge 212 and conducted through conduit 240 torepulping tank 242. Water is conducted through line 244 to repulpingtank 242. The mixture of water and solids containing residual light oilin repulping tank 242 is agitated by stirring device 246 and the fluidmixture is then withdrawn from the repulping tank by means of pump 248.Pump 248 delivers the aqueous mixture through line 250 to theevaporating region of first stage evaporator 190 of the overallthree-stage evaporator assembly where at least a portion of the water isconverted to steam, thereby directly contacting the light oil-ladensolids and facilitating the evaporation of light oil therefrom. Inevaporator 190 the residual light oil and part of the water are thusboiled off at a pressure which may typically be between about 2 and 10inches Hg absolute. The entering mixture of water and aqueous solidscontaining residual light oil is heated in evaporator 190 to atemperature in the range of about 70°-250° F. and preferably about90°-175° F., depending on the pressure in the evaporator. As mentionedabove, the first stage evaporator 190 is heted by a mixed vapor of steamand vaporized light oil from line 188 which is at a temperature about30°-40° F. higher than the temperature of the deoiled mixture of solidsin water. As set forth earlier, condensate of the heating vapor iswithdrawn from evaporator 190 through line 192. Water vapor and lightoil vapor formed as a result of evaporation of the entering mixture ofwater and solids containing residual light oil are removed from thevapor chamber of evaporator 190 through line 252 and conducted intosurface condenser 254 within which a partial vacuum is maintained bymeans of vacuum pump 256 which is connected to condenser 254 via vacuumline 258.

Surface condenser 254 is cooled by cooling water which enters thecondenser through line 260 and leaves the condenser through line 266.The mixed vapor of steam and vaporized light oil entering condenser 254through line 252 is condensed therein and the mixed condensate of waterand light oil is discharged from the condenser through line 184 andconducted thereby to oil-water separator 186.

The essentially completely deoiled slurry of solids in water from firststage evaporator 190 is continuously removed through line 268 with theassistance of pump 270. Pump 270 forces the slurry of solids in waterthrough line 268 to settling tank 272. The solids settle to the bottomof settling tank 272 from which they are removed as water-wet solidsthrough line 274 with the assistance of pump 276. Supernatant water isremoved from the top of settling tank 272 through line 244 and is forcedby pump 278 to repulping tank 242 where the water is mixed with solidscontaining residual light oil and is recycled through the system.

In oil-water separator 186 the mixture of water and light oil isseparated into light oil and partially clarified water containing somelight oil. The light oil phase is removed from oil-water separator 186through line 282 and is urged by pump 284 to light oil recycle tank 286from which it is forced by pump 288 via line 168 to fluidizing tank 164and thus recycled through the system. If the process provides a netyield of light oil, it may be recovered from tank 286 and stored for useoutside the system.

The partially clarified water is conducted from oil-water separator 186via line 290 to coalescer 292. Inside coalescer 292, the partiallyclarified water containing some light oil is separated into light oiland clean product water. The separated light oil is withdrawn fromcoalescer 292 through line 294, which meets line 282 at a "T" joint, andis ultimately conducted to light oil recycle tank 286. Clean productwater is withdrawn from coalescer 292 through line 296. The cleanproduct water may be used within the system or it may be removed tostorage for use outside the system.

Since the light oil is separated from extracted heavy oil before beingrecycled to fluidizing tank 164 an equilibrium does not occur, and theultimate result is the extraction of heavy oil from the water-insolublesolids by light fluidizing oil in centrifuge 212. The extraction of theheavy oil therefore reduces the final heavy oil content of the solidsproduct, a result which often increases the commercial value of thesolids for many uses.

FIG. 5 illustrates a portion of a modified apparatus of FIG. 1 whereinthe substantially anhydrous slurry of solids in light fluidizing oil isseparated by gravity into a light oil phase and a concentrated lightoil-solids slurry which is conducted directly to the deoiler apparatus.The gravity separation makes unnecessary a pressing apparatus such as acentrifuge for the separation of the substantially anhydrous slurry ofsolids in light fluidizing oil into its component parts.

In FIG. 5 a substantially anhydrous mixture of solids in lightfluidizing oil is withdrawn from third stage evaporator 76 and urged bypump 82 through line 84 to settling tank 300. The solids settle underthe force of gravity to the bottom of settling tank 300 from which theyare removed as a concentrated, pumpable light oil-solids slurry via line302. Pump 304, which is located on line 302, urges the concentratedoil-solids slurry through line 302 to deoiler apparatus 100.

Deoiler apparatus 100 may, if desired, be externally heated by steamjacket 102. Blowing steam generated in boiler-furnace 77 is conductedvia line 108 into deoiler apparatus 100 where the steam comes intodirect contact with the concentrated light oil-solids slurry and causesvaporization of the light oil at a temperature below its normal boilingpoint. Effluent blowing steam and vaporized light oil exit from thedeoiler apparatus through line 110 and are conducted to an evaporatorstage operating under reduced pressure as is described in FIG. 1. Valve126 which is equipped with a pressure sensor and which is located online 110 serves to maintain slightly less than atmospheric pressure indeoiler apparatus 100, i.e., essentially atmospheric pressure. Thesolids, free from light oil, are discharged from deoiler apparatus 100via conduit 114 and are treated in accordance with the proceduredescribed in FIG. 1.

Light fluidizing oil from the oil-water separator and the coalescer areconducted via line 48 into settling tank 300. The combined lightfluidizing oil is discharged from settling tank 300 through line 306 andis urged by pump 308, which is located thereon, to the fluidizing tankfor recycling through the system. If the process provides a net yield ofoil, it may be recovered from settling tank 300 and stored for useoutside the system.

In the foregoing description of FIG. 5, if the aqueous solids hadinitially contained a heavy, relatively non-volatile oil, it would nothave been completely extracted by the light fluidizing oil. Theconcentrated light oil-solids slurry pumped from settling tank 300 tothe deoiler apparatus would contain an appreciable fraction of thenon-volatile oil which would not be removed in the deoiler. Theessentially dry solids product would thus contain at least some heavy,non-volatile oil.

It will be understood by those skilled in the art that the modificationof FIG. 1 depicted in FIG. 5 wherein the deoiler apparatus is operatedat essentially atmospheric pressure is equally applicable to the casewhere the deoiler apparatus is operated at reduced pressure as isillustrated in FIG. 2. In either case an essentially dry solids productis obtained.

FIG. 6 depicts the apparatus of an embodiment of the invention wherein acompact, relatively simple system is employed. The apparatus ischaracterized by employment of a single stage evaporator and a settlingtank for the gravity separation of the substantially anhydrous slurry ofsolids in light fluidizing oil into an oil phase and a concentratedoil-solids slurry. The concentrated slurry is pumped to the deoilerapparatus where it is directly contacted with blowing steam. Effluentblowing steam and vaporized light oil from the deoiler apparatus areconducted to the single stage evaporator to supply evaporative heatthereto, a necessary expedient to achieve efficient steam utilization inthe compact system.

In FIG. 6 a stream of aqueous solids enters fluidizing tank 310 throughline 312. Light fluidizing oil enters fluidizing tank 310 through line314. The fluid mixture in fluidizing tank 310 is agitated by means ofstirring device 316 and is then withdrawn from the tank by means of pump318. Pump 318 forces the mixture through line 320 to the evaporatingregion of single stage evaporator 326. In evaporator 326 substantiallyall the water and a portion of the light oil are boiled off at apressure that is subatmospheric. The temperature of the product ofsingle stage evaporator 326, i.e., a slurry of solids in light oilcontaining about 1% by weight of water based on the entire slurry, iswithin the range of about 100°-400° F. and preferably about 150°-350°F., depending on the pressure in the evaporator. The heating medium forevaporator 326 is a mixture of steam and light oil vapor at atemperature about 30°-50° F. higher than that of the product, i.e., anessentially anhydrous slurry of solids in light oil. Steam for theevaporator is generated in boiler-furnace 328 and conducted toevaporator 326 through line 330. Also, a mixture of steam and light oilvapor is conducted to evaporator 326 from deoiler apparatus 332 via line334.

Condensate of the heating vapor is withdrawn through line 336 andconducted to oil-water separator 338. Mixed steam-light oil vapor formedas a result of the essentially complete dehydration of the enteringmixture of aqueous solids in light oil is removed from the vapor chamberof evaporator 326 through line 340 and conducted to surface condenser342 within which a partial vacuum is maintained by means of vacuum pump344 which is connected to surface condenser 342 via vacuum line 346.

The mixture of steam and light oil vapor entering surface condenser 342is condensed by cooling water entering the condenser through line 348and leaving the condenser through line 350. The mixed condensate of warmwater and light oil is discharged from the condenser through line 352into oil-water separator 338.

Inside oil-water separator 338, the mixture of water and light oil isseparated into light oil and partially clarified water containing somelight oil. The separated light oil is removed from oil-water separator338 through line 354 and is conducted thereby to settling tank 356.

The partially clarified water is conducted from oil-water separator 338via line 358 to coalescer 360. Inside coalescer 360, the partiallyclarified water containing some light oil is separated into light oiland clean product water. The separated light oil is withdrawn fromcoalescer 360 through line 362, which meets line 354 at a "T" joint, andis ultimately conducted to settling tank 356. Clean product water iswithdrawn from coalescer 360 through line 364. If desired, a portion ofthe clean product water may be withdrawn from coalescer 360 via line 366and conducted to boiler furnace 328 for reuse throughout the system.Alternatively, all the recovered clean water may be withdrawn throughline 364 and conducted to a reservoir for later use in applications inwhich essentially clean water is required.

The essentially anhydrous mixture of solids in light fluidizing oil iswithdrawn from single stage evaporator 326 and urged by pump 368 throughline 370 to settling tank 356. The solids settle under the force ofgravity to the bottom of settling tank 356 from which they are removedas a concentrated, pumpable light oil-solids slurry via line 372. Pump374, which is located on line 372, urges the concentrated oil-solidsslurry through line 372 to deoiler apparatus 332.

Deoiler apparatus 332 may, if desired, be externally heated by steamgenerated in boiler-furnace 328 which enters steam jacket 376 via line378. Condensate of the jacket steam is withdrawn through line 380, whichmeets line 366 at a "T" joint, and is ultimately returned to theboiler-furnace. Blowing steam generated in boiler-furnace 328 isconducted via line 378 to line 382, which is connected thereto by a "T"joint, and from line 382 into deoiler apparatus 332 where said blowingsteam comes into direct contact with the concentrated light oil-solidsslurry and causes vaporization of the light oil at a temperature belowits normal boiling point. Effluent blowing steam and vaporized light oilexit from the deoiler apparatus through line 334 and are conductedthereby to single stage evaporator 326 where the mixed vapor suppliesevaporative heat to said evaporator. Since evaporator 326 is operated atless than atmospheric pressure, a valve 383 which is equipped with apressure sensor is located on line 334 and serves to maintain slightlyless than atmospheric pressure in deoiler apparatus 332. The deoilingstep in the illustrated embodiment is therefore conducted at essentiallyatmospheric pressure. Alternatively, the effluent blowing steam andvaporized light oil may be used for preheating the aqueous solids-lightfluidizing oil mixture by injection into fluidizing tank 310 or, indeed,at any other location in the system where recovery of its energy canoffer process credits. The use of this mixed vapor to supply evaporativeheat to the single stage evaporator or elsewhere in the system isnecessary to achieve efficient steam utilization in the compactapparatus depicted in the embodiment of FIG. 6.

The solids, free from light fluidizing oil, are discharged by gravityfrom deoiler apparatus 332 through conduit 384 into live bottom bin 386.The screw conveyor bottom of bin 386 conducts the solids to the exitthereof where said solids, free from the light fluidizing oil as well asbeing in an essentially anhydrous state, are discharged through line 388into grinder or comminuter 390. By means of grinder 390 the solids arereduced to granular if not powder form, and from the grinder they flowthrough line 392 to a rotary selector valve 394 by which they may bedirected to either line 396 or line 398. Line 396 leads to collecting orbagging equipment, and through it the solids may be withdrawn for useoutside the illustrated system. Line 398, shown as active according tothe setting of valve 394, leads to the suction of blower 400, and theblower discharges the comminuted solids through line 402 to thecombustion region of boiler-furnace 328.

As indicated above, the essentially anhydrous mixture of solids in lightfluidizing oil in settling tank 356 separates under the force of gravityinto a lower solids phase and a supernatant light oil phase. The solidsare removed from the settling tank as a concentrated light oil-solidsslurry and conducted to deoiler apparatus 332. The supernatant lightfluidizing oil is discharged from settling tank 356 through line 314 andis urged by pump 404, which is located thereon, to fluidizing tank 310for recycling through the system. If the process provides a net yield ofoil, it may be recovered from settling tank 356 and stored for useoutside the system.

As described above in connection with the description of FIG. 5, if theaqueous solids had initially contained a heavy, relatively non-volatileoil, it would not have been completely extracted by the light fluidizingoil. As a result, the essentially dry solids product of the embodimentof this invention illustrated in FIG. 6 would contain at least someheavy, non-volatile oil.

Since the flow diagrams as shown in the drawings have been discussedabove in connection with the dehydration and subsequent deoiling ofaqueous solids generally, it will be understood by those skilled in theart that our invention may be used to advantage in the dehydration in alight oil medium, followed by gross deoiling, of aqueous waste solidsand aqueous solids having intrinsic value. Examples of such aqueoussolids are sewage sludge, slaughter house effluent and renderingmaterials, inorganic salts, pharmaceutical products, certain tree barks,the organic streams from garbage disposal plants, various aqueouschemicals and mixtures thereof, animal feeds, and food products forhuman consumption.

Thus, the instant invention provides process and apparatus for therecovery of clean water and solids from aqueous solids dehydrated in alight fluidizing oil medium that is immiscible with water. The processis characterized by the recovery of residual light fluidizing oil fromsaid solids after the dehydration thereof. Following the dehydrationstep, the concentrated light oil-solids slurry or the light oil-ladensolids are brought into direct contact with blowing steam. The blowingsteam, if superheated, supplies latent heat for the evaporation of theresidual light fluidizing oil and furthermore, since the light oil iswater-immiscible, its direct contact with the blowing steam amountsessentially to a steam distillation wherein the light oil in thepresence of blowing steam boils at a temperature below its normalboiling point. The light fluidizing oil may be evaporated from thesolids at even lower temperatures by being contacted with blowing steamat subatmospheric pressures. As a result of such reduced pressures, notonly is the light oil more readily evaporated from the solids with lessheat energy being required, but it makes possible the use of higherboiling light fluidizing oils. Furthermore, this invention makespossible the winning of solids that are not only dehydrated but whichare deoiled beyond the point usually attainable by mechanical means.Moreover, if the aqueous solids feed is initially associated with aheavy, relatively non-volatile oil, embodiments of the instant inventionmake possible its substantial removal from the solids product where itmay, if it has value, be used outside the system. On the other hand, ifthe heavy oil initially associated with the aqueous solids is notseparated from the light fluidizing oil prior to its being recycledthrough the system, an equilibrium is set up whereby the heavy oilcontent of the dehydrated product remains essentially the same as thatof the feed material on a water-free basis.

While specific embodiments of the present invention have been shown anddescribed in detail to illustrate the utilization of the inventiveprinciples, it is to be understood that such showing and descriptionhave been offered only by way of example and not by way of limitation.Protection by Letters Patent of this invention in all its aspects as thesame are set forth in the appended claims is sought to the broadestextent that the prior art allows.

We claim as our invention:
 1. A process for the recovery of clean waterand substantially fluidizing oil-free solids from water-insolubleaqueous solids originally associated with a heavy, relativelynon-volatile oil and dehydrated in an oil medium comprising the steps of(1) admixing an aqueous slurry of said solids with a low viscosity,relatively volatile, water-immiscible light fluidizing oil to obtain amixture which will remain fluid and pumpable after the removal of thewater content therefrom; (2) subjecting the resultant oil-containingmixture to dehydration by heat evaporation whereby substantially all thewater and part of the light fluidizing oil are vaporized, yielding amixed water and light oil vapor and a substantially anhydrous solids inoil slurry; (3) condensing said mixed water and light oil vapor; (4)separating the resultant condensate into a clean water fraction and alight oil fraction; (5) expressing at least some of the relativelyvolatile, water-immiscible light fluidizing oil and extracted heavy oilfrom said substantially anhydrous solids in oil slurry; (6) slurryingthe resultant solids carrying residual light fluidizing oil with water;(7) heating the resultant slurry to convert a portion of said water toblowing steam which directly contacts said solids carrying residuallight fluidizing oil, thereby facilitating the removal of substantiallyall the light oil therefrom; (8) allowing the solids in the resultantwater-solids slurry to settle under the force of gravity; (9) removingthe supernatant water from the settled solids, said solids having areduced heavy oil content; (10) dividing the expressed light oil andextracted heavy oil of step (5) into a light oil fraction and a heavyoil fraction, and (11) combining the light oil fraction of step (10)with the separated light oil fraction of step (4) and admixing thosecombined fractions with fresh aqueous solids and thereby recycling themthrough the process as fluidizing oil.
 2. The process of claim 1 whereinheat evaporation step (2) is carried out at temperatures within therange of about 100° F. to 400° F., and heating step (7) is carried outat temperatures within the range of about 70° F. to 250° F.
 3. Anapparatus for recovering clean water and substantially oil-free solidsfrom water-insoluble aqueous solids dehydrated in a light fluidizing oilmedium with said aqueous solids being originally associated with aheavy, relatively non-volatile oil, said apparatus comprising (1) a tankadapted to receive a stream of said aqueous solids and provided with astirring or mixing mechanism, (2) a light fluidizing oil reservoir, (3)means for transmitting light fluidizing oil from said light oilreservoir to said tank wherein said light fluidizing oil and aqueoussolids may be mixed, (4) a multi-stage dehydrating evaporator comprisingat least first and second stages, (5) a conduit extending from said tankto the second stage of said multi-stage dehydrating evaporatorwherethrough may flow a stream of aqueous solids admixed with lightfluidizing oil from said tank into the evaporating region of the secondstage of said multi-stage dehydrating evaporator to serve as feedmaterial therefor, (6) a conduit extending from the vapor chamber of thesecond stage of the dehydrating evaporator to the evaporating region ofthe first stage thereof through which may flow a mixture of water vaporand light oil vapor formed as a result of heat evaporation of saidaqueous solids and light fluidizing oil mixture to thereby act as asource of evaporative heat in said first stage, (7) a liquid-solidseparating means, (8) a conduit extending from the second stage of saiddehydrating evaporator to said liquid-solid separating meanswherethrough may flow a stream of a substantially anhydrous slurry ofwater-insoluble solids in light fluidizing oil, (9) an oil tank, (10) aconduit extending from said liquid-solid separating means to said oiltank wherethrough may flow a mixture of light fluidizing oil and heavyoil extracted from said solids, (11) a stripping evaporator wherein thelight fluidizing oil and any incidentally associated water or watervapor may be separated from said oil mixture by heat evaporation, (12) aconduit extending from said oil tank to said stripping evaporatorwherethrough may flow said oil mixture to serve as feed material to theevaporating region of that evaporator, (13) condensing means, (14) aconduit extending from the vapor chamber of said stripping evaporator tosaid condensing means wherethrough may flow a mixture of water vapor andlight oil vapor formed by heat evaporation in said stripping evaporator,(14) an oil-water separating means, (15) a conduit extending from saidcondensing means to said oil-water separating means wherethrough mayflow a mixed condensate of water and light oil from said condensingmeans to said oil-water separating means wherein said mixed condensatemay be separated into a clean water product and light oil, (16) arepulping tank provided with a mixing or stirring device, (17) a conduitextending from said liquid-solid separating means to said repulping tankthrough which may flow solids carrying residual light fluidizing oil,(18) a settling tank disposed to serve as a water reservoir, (19) aconduit extending from said settling tank to said repulping tankwherethrough may flow water to be admixed with said solids carryingresidual light fluidizing oil in said repulping tank, (20) a conduitextending from said repulping tank to the first stage of saidmulti-stage dehydrating evaporator wherethrough may flow an aqueousslurry of said water-insoluble solids carrying residual fluidizing oilfrom said repulping tank into the evaporating region of said first stageof the dehydrating evaporator to serve as feed material therefor, (21) acondenser distinct from said condensing means (13), (22) a conduitextending from the vapor chamber of said first stage of the dehydratingevaporator through which may flow water vapor and light oil vapor formedas a result of heating said aqueous slurry of solids carrying residuallight fluidizing oil, (23) a conduit extending from said condenser tosaid oil-water separating means wherethrough may flow a mixed condensateof water and light oil from said condenser to said oil-water separatingmeans for mixing with the oil-water condensate returned to saidoil-water separating means from condensing means (13) and, along withthat first-designated condensate, separation into a clean water productand light oil, (24) a conduit extending from said first stage of thedehydrating evaporator to said settling tank wherethrough may flow anaqueous slurry of solids and any residually associated light fluidizingoil from said first stage of the dehydrating evaporator to said settlingtank wherein that slurry may be separated into wet solids andsupernatant water, (25) means for separately withdrawing light oil andclean water from said oil-water separating means, and (26) a conduitextending from said withdrawing means to said light fluidizing oilreservoir (2) wherethrough may flow a stream of light oil as feedmaterial to that reservoir for recycling therefrom to said tank (1). 4.The apparatus of claim 3 which further comprises a combustion apparatusassociated with said multi-stage dehydrating evaporator and saidstripping evaporator for supplying evaporative heat thereto.
 5. Theapparatus of claim 3 wherein said liquid-solid separating means is acontinuous centrifuge.